A tooth is basically divided into two parts, the visible part of your teeth which is called crown and the invisible part of your teeth which is called roots. These roots are present below the gum line of your teeth and help the teeth to get attached to the bone. A tooth has four layers and all the four layers have different functions. These four layers are enamel, dentin, cementum, and pulp.
The upper layer of your is enamel which the visible and white thing of your teeth that covers your teeth. This enamel layer is harder than bone which protects the vital tissue within the teeth. This enamel layer is made by of Hydroxyapatite, Phosphorus, and Calcium.
The enamel layer is further followed by the dentin layer of the teeth which get converted into Calcium Carbonate and other Calcium products that looks like something similar to a bone. Dentin is not that hard as enamel is and thus it has a greater risk to get decayed.
This dentin layer is further followed by the cementum layer which is also the second last layer of your teeth. This cementum layer covers the root and acts as a base for the teeth to get attached to the bone. It is softer than enamel and dentin of your teeth and is covered by the gums and bones of your teeth.
The last but not the least layer of your teeth is pulp. The pulp is found in the core of your teeth which includes all the soft tissues with the nerves and blood vessels of your teeth which gives nutrition to your teeth.